This invention relates, in general, to electroluminescent systems, and more specifically to a membranous monolithic urethane electroluminescent structure whose monolithic phase comprises a series of contiguous electroluminescent layers deployed using a unitary vinyl gel resin carrier that is catalyzed to transform into a unitary urethane carrier during curing.
Electroluminescent (xe2x80x9cELxe2x80x9d) lighting has been known in the art for many years as a source of light weight and relatively low power illumination. Because of these attributes, electroluminescent lamps are in common use today providing light for displays in, for example, automobiles, airplanes, watches, and laptop computers. One such use of electroluminescence is providing the back light necessary to view Liquid Crystal Displays (LCD).
Electroluminescent lamps may typically be characterized as xe2x80x9clossyxe2x80x9d parallel plate capacitors of a layered construction. Electroluminescent lamps of the current art generally comprise a dielectric layer and a luminescent layer separating two electrodes, at least one of which is translucent to allow light emitted from the luminescent layer to pass through. The dielectric layer enables the lamp""s capacitive properties. The luminescent layer is energized by a suitable power-supply, typically about 115 volts AC oscillating at about 400 Hz, which may advantageously be provided by an inverter powered by a dry cell battery. Electroluminescent lamps are known, however, to operate in voltage ranges of 60 V-500V AC, and in oscillation ranges of 60 Hz-2.5 KHz.
It is standard in the art for the translucent electrode to consist of a polyester film xe2x80x9csputteredxe2x80x9d with indium-tin-oxide (ITO). Typically, the use of the polyester film sputtered with ITO provides a serviceable translucent material with suitable conductive properties for use as an electrode.
A disadvantage of the use of this polyester film method is that the final shape and size of the electroluminescent lamp is dictated greatly by the size and shape of manufacturable polyester films sputtered with ITO. Further, a design factor in the use of ITO sputtered films is the need to balance the desired size of electroluminescent area with the electrical resistance (and hence light/power loss) caused by the ITO film required to service that area. Generally, a large electroluminescent layer will require a low resistance ITO film to maintain manageable power consumption. Thus, the ITO sputtered films must be manufactured to meet the requirements of the particular lamps they will be used in. This greatly complicates the lamp production process, adding lead times for customized ITO sputtered films and placing general on the size and shape of the lamps that may be produced. Moreover, the use of ITO sputtered films tends to increase manufacturing costs for electroluminescent lamps of nonstandard shape.
The other layers found in electroluminescent lamps in the art are suspended in a variety of diverse carrier compounds (often also referred to as xe2x80x9cvehiclesxe2x80x9d) that typically differ chemically from one another. As will be described, the superimposition of these carrier compounds upon one another and on to the sputtered ITO polyester film creates special problems in the manufacture and performance of the lamp.
The electroluminescent layer typically comprises an electroluminescent grade phosphor suspended in a cellulose-based resin in liquid form. In many manufacturing processes, this suspension is applied over the sputtered ITO layer on the polyester of the translucent electrode. Individual grains of the electroluminescent grade phosphor are typically of relatively large dimensions so as to provide phosphor particles of sufficient size to luminesce strongly. This particle size, however, tends to cause the suspension to be non-uniform. Additionally, the relatively large particulate size of the phosphor can cause the light emitted from the electroluminescent to appear grainy.
The dielectric layer typically comprises a titanium dioxide and barium-titanate mixture suspended in a cellulose-based resin, also in liquid form. Continuing the exemplary manufacturing process described above, this suspension is typically applied over the electroluminescent layer. It should be noted that for better luminescence, the electroluminescent layer generally separates the translucent electrode and the dielectric layer, although those in the art will understand that this is not a requirement for a functional electroluminescent lamp. It is possible that unusual design criteria may require the dielectric layer to separate the electroluminescent layer and the translucent electrode. It should also be noted that, occasionally, both the phosphor and dielectric layers of the lamps in the art utilize a polyester-based resin for the carrier compound, rather than the more typical cellulose-based resin discussed above.
The second electrode is normally opaque and comprises a conductor, such as silver and/or graphite, typically suspended in an acrylic or polyester carrier.
A disadvantage of the use of these liquid-based carrier compounds standard in the art is that the relative weight of the various suspended elements causes rapid separation of the suspension. This requires the frequent agitation of the liquid solution to maintain the suspension. This agitation requirement adds a manufacturing step and a variable to suspension quality. Furthermore, liquid carrier compounds standard in the art tend to be highly volatile and typically give off noxious or hazardous fumes. As a result, the current manufacturing process must expect evaporative losses in an environment requiring heightened attention to worker safety.
A further disadvantage in combining different carrier compounds, as is common in the art, is that the bonds and transitions between the multiple layers are inherently radical. These radical transitions between layers tend strongly to de-laminate upon flexing of the assembly or upon exposure to extreme temperature variations.
A still further disadvantage in combining different carrier compounds is that different handling and application requirements are created for each layer. It will be appreciated that each layer of the electroluminescent lamp must be formed using different techniques including compound preparation, application, and curing techniques. This diversity in manufacturing techniques complicates the manufacturing process and thus affects manufacturing cost and product performance.
The disclosure of application Ser. No. 09/173,521, incorporated herein by reference, addresses many of the foregoing needs in the electroluminescent art by providing an electroluminescent system having monolithic structure via use of a unitary vinyl resin vehicle in deployed gel form. This vinyl-based monolithic structure is also disclosed in an exemplary embodiment of the membranous electroluminescent devices taught by application Ser. No. 09/173,404, the disclosure of which application is also incorporated herein by reference. Specifically, 09/173,404 teaches exemplary use of the vinyl-based monolithic structure as an electroluminescent laminate deployed between two membranous urethane envelope layers.
While the electroluminescent systems described in Ser. Nos. 09/173,521 and 09/173,404 have been found to be serviceable, it will be appreciated that yet further advantages of monolithic structure could be obtained if the electroluminescent laminate in Ser. No. 09/173,404 had layers suspended in a urethane carrier. In this way, the membranous electroluminescent devices disclosed in 09/173,404 would comprise layers in the electroluminescent laminate that were in monolithic unity with surrounding urethane envelope layers.
It will be understood, however, that in manufacturing and deployment terms, urethane is a less than optimal carrier for electroluminescent systems, lacking many of the advantages taught by the vinyl resin gel vehicle disclosed in application Ser. No. 09/173,521. Accordingly, there is a need in the art for an electroluminescent system that can be constructed using a unitary common carrier comprising vinyl resin in gel form which then, when cured, acquires monolithic unity with urethane envelope layers such as disclosed in Ser. No. 09/173,404.
The present invention addresses the above-described problems by suspending selected layers of a membranous electroluminescent system, prior to deployment, in a carrier comprising (1) a vinyl resin in gel form and (2) a polymeric hexamethylene diisocyanate catalyst. During curing, the catalyst facilitates transformation of the vinyl resin carrier into a urethane. Once cured, the transformed urethane carrier compound enables electroluminescent layers to bond in a monolithic structure also comprising other contiguous urethane layers, such as envelope layers. As a result, membranous electroluminescent structures made in accordance with the present invention are even stronger, and even less prone to de-lamination than their predecessors. A high degree of crosslinking becomes available between neighboring urethane layers.
As noted, a preferred embodiment of the present invention initially uses a vinyl resin in gel form as the unitary carrier compound during deployment of the inventive inks. This choice of carrier is surprisingly contrary to the expected teachings of the prior art. As noted above, a functional electroluminescent lamp requires a dielectric layer to enable capacitive properties. Vinyl resin is not commonly used as a dielectric material and, thus, its utilization is counter intuitive. This choice of carrier has further, and somewhat serendipitously, proven to be compatible with a wide variety of substrates, including metals, plastics and cloth fabrics. Moreover, unlike traditional carrier compounds, vinyl gel is highly compatible with well-known manufacturing techniques such as screen printing.
These and other advantages of deploying electroluminescent inks in vinyl gel resin are thus retained by the invention. Once deployed, however, the catalyst added to the vinyl resin-based ink converts the vinyl to urethane, enabling a high degree of crosslinking in the cured laminate between converted ink layers and other contiguous urethane layers. This high degree of crosslinking is available between neighboring cured urethane layers regardless of whether the urethane layer was deployed as a urethane or as a catalyzed vinyl.
One application of the presently preferred embodiment is in the apparel industry. It will be readily appreciated that the membranous electroluminescent system as disclosed herein may be applied by conventional screen printing techniques to transfer release paper or silicon-coated polyester sheet to allow a membranous xe2x80x9ctransferxe2x80x9d to be constructed. A suitable adhesive then allows rugged electroluminescent designs of virtually limitless shape, size and scope to be affixed to a very wide range of garments and attire. This application should be distinguished from apparel techniques previously known in the art where pre-manufactured electroluminescent lamps of predetermined shape and size were combined and affixed to apparel by sewing, adhesive, or other similar means. It will be understood that the present invention distinguishes clearly from such techniques in that, unlike prior systems, the fabric of the apparel is used as the substrate for the electroluminescent system.
It will also be understood that the present invention is expressly not limited to apparel applications. As noted, the present invention is compatible with a very wide range of substrates and thus has countless further applications, including, but not limited to, emergency lighting, instrumentation lighting, LCD back lighting, information displays, cellular telephone keypads, backlit keyboards, etc. In fact, the scope of this invention suggests strongly that in any application where, in the past, information or visual designs have been communicable by passive ink applied to a substrate, such applications may now be adapted to have that same information enhanced or replaced by electroluminescence.
It will be further appreciated that accessories standard in the art maybe combined with the present invention to widen yet further the scope of applications thereof. For example, dyes and/or filters may be applied to obtain virtually any color. Alternatively, timers or sequencers may be applied to the power supply to obtain delays or other temporal effects.
It will be further appreciated that, while a preferred embodiment of the present invention involves application by screen printing techniques, any number of application methods will be suitable. For example, individual layers may alternatively be applied to a substrate by spraying under force from a nozzle not in contact with the substrate. It should be further noted that, according to the present invention, each of the layers comprising the electroluminescent system of the present invention may even be applied in a fashion different from its neighbor.
Accordingly, a technical advantage of the present invention is that the inventive inks have the advantages of vinyl resin inks in gel form during deployment, as well as the advantages of urethane inks after curing. Although deployed in vinyl form, cured neighboring layers of the present invention are catalyzed to transform into urethane form, causing them to bond inherently strongly to each other and to surrounding urethane layers, such as envelope layers. Such strong bonds are made available by having a unitary carrier in final form, and by crosslinking between urethane layers. The resulting monolithic structure of the present invention is highly rugged. The resulting monolithic structure is also membranous, having all the advantages of such membranous structures disclosed in application Ser. No. 09/173,404.
A further technical advantage of the present invention is that by initially using a unitary vinyl resin carrier in gel form for multiple layers, manufacturing tends to be simplified and manufacturing costs will be inevitably reduced. Only one carrier compound need be purchased and handled in a preferred embodiment of the present invention. Furthermore, layer application and materials handling, including equipment cleanup, is simplified, since each layer may be applied by a like process, will require similar conditions to cure, and is cleanable with the same solvents.
A still further technical advantage of the present invention is that the initial carrier, being a gel, maintains continued full suspension of the non-catalytic ingredients long after the initial mixing thereof. It will be understood that such maintained suspension results in savings in manufacturing costs because the ingredients tend not to settle out of the suspension, eliminating the need for re-agitation.
Furthermore, a gel carrier in initial form tends to reduce spoilage, since gels are less volatile than carrier compounds used traditionally in the art. Spoilage is reduced further by the increased suspension life as described above. The requirement in the art for frequent agitation of volatile carrier compounds tends to encourage evaporation of the carrier compounds. By eliminating the need for frequent agitation, less carrier compound will tend to evaporate.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.